Enterprise NX-01 operated five plasma injectors. When the fifth one started to fail in 2152, Enterprise acquired one replacement and two spares from the Kreetassans after a lengthy negotiation process, although the ship could have continued normal operation with only four working injectors. (ENT: "A Night in Sickbay")

In 2153, Skalaar contacted Gaavrin, his brother, and told him he had captured Jonathan Archer. He planned to hand Archer over to the Klingon Empire for 9,000 darseks, which he thought was enough to get his ship, the Tezra back. Gaavrin told him that the reward wouldn't change his decision to help his brother, to which Skalaar asked him if he wanted to scrub plasma injectors for the rest of his life. (ENT: "Bounty")

Later that year, Lorian, Charles Tucker III's son from an alternate timeline, stole all five of Enterprise's plasma injectors from the injector assembly for use on his Enterprise so he could meet with Degra in Jonathan Archer's place. Lorian did this to reduce the chance of Enterprise being thrown again to the year 2037 in the Kovaalannebula. Earlier, Enterprise had gained upgrades from Haradin traders for the plasma injectors to allow Enterprise to travel at warp 6.9 for brief periods. Lorian's Enterprise could not reach this speed as the plasma injectors were too old. (ENT: "E²")

In 2372, while running a shuttle simulation with Kes on Voyager's holodeck, Tom Paris clogged up the plasma injectors on the shuttlecraft to make the simulation more difficult. Kes referred to it as a "dirty trick". (VOY: "Parturition")